Peen plating

ABSTRACT

A process for metal plating which comprises spraying a mixture of metallic powder and small peening particles at high velocity against a surface, said velocity being sufficient to impact and bond said metallic powder onto said surface. In the case of metal surfaces, the process has as one of its advantages providing mechanical working (hardening) of the surface simultaneously with the metal plating.

United States Patent Babecki et al.

[451 Aug. 28, 1973 PEEN PLATING inventors: Alfred J. Babecki, Oxon Hill;Carl L.

Haehner, Laurel, both of Md.

The United States of America as represented by the Administrator of theNational Aeronautics and Space Administration, Washington, DC.

Filed: Dec. 6, 1971 Appl. No.: 205,047

Assignee:

U.S. Cl 117/105, 29/5272, 72/53, 1 17/66, 1 17/1055, 1 17/130R,1l7/l38.8 R, 117/151, 117/160 R Int. Cl 844d l/02 Field of Search117/104 B, 105, 105.5, 117/50, 66,130 R, 151,160 R, 138.8 R; 29/5272:72/53 References Cited UNITED STATES PATENTS Claus 117/104 B Schrewelius117/105.5 X Daniels 117/l05.5 X

Primary Examiner-Edward G. Whitby A!torney-R F. Kempf, John R. Manninget a1.

[57] ABSTRACT A process for metal plating which comprises spraying amixture of metallic powder and small peening particles at high velocityagainst a surface, said velocity being sufficient to impact and bondsaid metallic powder onto said surface.

In the case of metal surfaces, the process has as one of its advantagesproviding mechanical working (hardening) of the surface simultaneouslywith the metal plating.

10 Claims, 4 Drawing Figures /GLASS BEADS AND METAL POWDER PEEN PLATINGORIGIN OF THE INVENTION The invention described herein was made byemployees of the United States Government and may be manufactured andused by or for the Government for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Field of the Invention This inventionrelates to the metal plating of substrates such as metal substrates.More particularly, the present invention is directed to the depositionof metallic coatings on other substrates by peening metallic powder ontothe surface of the substrates.

Description of the Prior Art Numerous methods are known in the art forthe metallic plating or coating of substrates. Among these methods canbe mentioned application of metallic coatings by electro chemical andchemical deposition in tanks of aqueous solutions of metal salts, byimmersion into molten baths of the metal and by spray and brushapplication as a paint.

Although these prior art techniques have enjoyed some commercial successthey are not without their shortcomings. Many of the prior arttechniques, for instance, involve the use of hazardous chemicals and/orfumes. Others are characterized by less than desirable deposition ratesand a tendency to cause hydrogen embrittlement. Most of the prior artmethods, moreover, are limited in the number of substrates they arecapable of coating. Another common complaint heard against certain priorart techniques is the complexity and costliness of the equipmentrequired. Lastly, all of the aforementioned prior techniques do noteffect any mechanical working (hardening) of the substrate surface and,therefore, do not benefit from such working.

One object of the invention is to provide a method for metal platingsurfaces which does not involve hazardous chemicals and/or fumes andwhich precludes the possibility of hydrogen embrittlement.

Another object of the invention is to provide a process which plates ata more rapid rate than prior art methods and does not require complex orcostly equipment to operate.

Yet another object of theinvention is to provide a process for thedeposition of a metallic coating which simultaneously effects adesirable mechanical working (hardening) of the substrate surface.

A further object of the invention is to provide a process for themetallic coating of substrates wherein the substrate surface isconveniently preconditioned before the metallic coating is applied.

These and other objects of the invention will become apparent or will bepointed out with particularity as the description proceeds.

BRIEF SUMMARY OF THE INVENTION In accordance with the process of theinvention the surface of a substrate is metal plated by spraying thesurface with a mixture of metallic powder and small peening particles ata high velocity sufficient to impact and bond the metallic powder ontothe surface.

Another aspect of the invention involves first preconditioning thesurface of the substrate by effecting the spraying without the metallicpowder and then subse quently introducing the metallic powder into thestream of small peening particles to form the admixture sprayed atpeening velocity against the surface to be plated.

Still another aspect of the invention involves plating the substrateswith two or more metal powders fed simultaneously or alternately intothe stream of peening particles or with metal and non-metal powderssimilarly applied, to effect mixtures or layers onto the substratesurface.

Without being bound by any theory or scientific explanation of howprecisely the present invention effects the uniform metal plating, it isbelieved that, for the most part, the following sequence of eventsoccurs in rapid succession many times through the spraying operation: l)the peening particles create a multitude of depressions or peenedcavities in the substrate surface which depressions may be said toresemble oceanic waves 2) metallic powder from the spray stream settlesin the depressions or peened cavities and is pounded in by the next orensuing peening particle or particles. In the case of metal surfaces,the peening of the surface that occurs prior to and simultaneously withthe metal plating or coating constitutes a mechanical working(hardening) of the substrate surfaces which improves the substrate, forinstance, by l) hardening the surface, 2) introducing compressiveresidual stresses for fatigue improvement, 3) eliminates tool marks,etc.

DETAILED DESCRIPTION OF THE INVENTION The means for spraying the mixtureof metallic powder and peening particles may comprise, for instance, anysuitable air or other gas pressured equipment that is capable ofpropelling powder and peening particles as a spray stream at a peeningvelocity. Essentially the same techniques as are involved in sandblasting are applicable to the spray step of the invention. Alternately,airless means for the propulsion of peening media can be used. Thisairless method of peening media propulsion incorporates a rotating wheelwith hoppers located around its perimeter. The speed of rotation of thewheel determines the intensity with which the media strikes the partbeing processed. Thus, with regard to the means for spraying the mixtureof metallic powder and peening particles, the only essentialconsideration is that the equipment be capable of spraying out the smallparticles at peening velocity. By peening velocity" is meant a velocitysufficient to cause the substrate surface to be cleaned and to effectminute depressions in the surface and to cause bonding of the metallicpowder to the surface. Hence, the design of the nozzles used to directthe stream of metallic powder and peening particles can varyconsiderably as shown in the attached drawing wherein:

FIG. 1 is a sectional view of a spray nozzle useful in the process ofthe invention whose design is such that the mixture of metallic powderand peening particles pass through its entire length;

FIG. 2 is a sectional view of another type of spray nozzle meanscomprising a primary nozzle through which the peening particles arepassed and a separate secondary nozzle by which the metallic powder isintroduced;

FIG. 3 is yet another type of spray nozzle means which may be used inthe process of the invention comprising a primary nozzle through whichthe peening particles are introduced and a separate secondary nozzlearranged to direct metallic powder into the stream of peening particlesoutside the primary nozzle; and

FIG. 4 represents the embodiment of the invention wherein a plurality ofthe spray nozzle means of FIG. 1 are employed.

Referring to FIG. 1, a conduit 3 is attached to a source of compressedair (not shown) to provide a blast of air that propels the mixture ofmetal powder and particles. A spray nozzle 6 is fitted onto conduit 3for directing the air spray. A supply of small spherical particles suchas glass beads 9 and metallic powder 12 are admixed in a hopper (notshown) and both propelled first through conduit 3 and then nozzle 6,exiting as a spray stream which impinges upon a substrate 15.

Directing attention to FIG. 2, the design of the spray nozzle meansdepicted therein is identical to that of FIG. 1 except that a secondaryspray nozzle 17 is threadedly engaged to spray nozzle 6 for the separateintroduction of metal powder within the nozzle head of spray nozzle 6which separately introduces the small glass beads.

The spray nozzle means of FIG. 3 is identical in design to that of FIG.1 except that a separate external secondary spray nozzle 17 is arrangedto introduce the metallic powder directly into the spray stream of thepeening particles emanating from spray nozzle 6.

In FIG. 4 a plurality of the spray nozzle means of FIG. 1, eachcomprised of a conduit 3 attached to a source of compressed air and anozzle 6, are inwardly directed to spray the mixture against thesubstrate 15.

It also should be understood that the size of the nozzle apertures canbe varied. Additionally, one nozzle with two or more ports and'separatevalving can be used with separate air pressures to direct the variousstreams to form one in fornt of the nozzle, or two or more individualnozzles can be employed to obtain the same effect.

Although the preferred small peening particles of the invention arespherical peening particles such as glass beads, other suitable peeningparticles include metal shot, ceramic beads and the like. Further, thepeening particles need not necessarily be spherical in shape and cantake the form as generally commercially available. The sizes of thepeening particles that may be used in the process can be those of theconventional beads used for peening and blast cleaning. Ordinarily, thepeening particles range in size from about 0.0661 inch in diameter toabout 0.0010 inch in diameter. However, for large and thick substrates,even larger beads to about 0.1000 inch diameter may be used withproperly sized equipment.

Any metallic powder of varying degrees of hardness and particle shape,(for instance, flake or spherical) is contemplated for use as thecoating material in the present invention. Illustrative of metallicpowders that may be used are aluminum, nickel, silver, gold, tungsten,copper, zinc, etc. In general, the size of commercially availablemetallic powders will range from about l mesh to +270 mesh, any one ofwhich is suitable for use in the process of the invention. The metallicpowder size selected, however, should be no larger than about one halfthe peening particle size for good coating. The precise size of metallicpowder employed will depend in large part upon practical considerationssuch as the speed of the process and the thickness of coating desired.Should, for example, a thin layer of plated metal be desired, a sizeratio of metal powder to peening particle down to about 1:20 can beemployed.

A unique feature of the invention is that two or more different metallicpowders can be introduced into the peening particle streamsimultaneously or alternately; or metal and non-metal powders can beapplied together or in layers. This feature has been found to offer anumber of practical uses and advantages. For instance, one stream couldbe a soft metal powder to provide electrical or thermal conduction andthe other stream could be a hard metal powder to provide wearresistance.

The proportions of peening particles to metallic powder employed in theprocess may vary widely, the proportions selected depending primarilyupon the substrate, the pressure used and the degree of peening orcoating desired. If, for instance, it is desired to minimize peening andmaximize plating a ratio of metallic powder to peening particles ofabout 50:50 can be employed. Although ratios of powder to peeningparticles in excess of 50:50 are employable they generally areunnecessary and frequently constitute a waste of metallic powder. On theother hand, if it is desired to maximize peening and minimize platingratios of metallic powder to peening particles less than 50:50, down to.for example, 10:90 may be selected.

As aforementioned, the air or other gas pressure employed in thespraying of the metallic powder and peening particles is that sufiicientto maintain free continuous flow and produce a peening effect at thedistance the spray nozzle is held from the substrate or workpiece. Theparticular pressure employed in a given operation depends on severalfactors such as the hardness of the substrate, the distance the spraynozzle is held from the piece, the size and proportions of the metallicpowder and peening particles and whether peening or plating is to befavored. Also, the pressure may be varied during the course of theoperation. For instance, it may be desired to operate initially at ahigh pressure to clean the surface or to produce an intensity thathardens and introduces compressive residual stresses into the substrate,elminates tool marks, etc., and then reducing the intensity by loweringthe pressure to complete the plating operation.

The force intensity of the peening media (metallic powder and peeningparticles) can be varied by the air (or gas) pressure, the distance ofthe part from the nozzle, the rate of flow of the peening plating mediainto the air stream, the orifice size of the nozzle or any combinationof these variables.

The substrates which can be metal plated or coated in accordance withthe present invention include any hard material having a peenablesurface. Such materials include metals and alloys, such as copper,steel, magnesium, aluminum alloys, etc., wood, plastics such as nylon,polyethylene, polypropylene, polymethacrylates, etc., fiberglass,ceramics, and the like.

In the embodiment of the invention wherein the surface of the substrateor workpiece is preconditioned by first effecting the spraying with thepeening particles alone before introduction of the metallic powder intothe stream, the preconditioning may take different forms. One form cancomprise a surface cleaning operation whereby the part to be coated iscleaned with a gentle or low angle stream of peening particles to removemst, scale, paint, etc., before introduction of the metallic powder intothe stream, thereby improving adhesion of the coating. Another form, inthe case of a metal surface involves peening with a high angle stream ofpeening particles to induce compressive stresses for fatigue and stresscorrosion resistance, again before the flow of metal powder is begun.Yet another form, also in the use of metal surfaces, comprises acombination of the surface cleaning step followed by the peening stepbefore the metal powder is cut into the stream.

The plating process is preferably conducted in a suitable cabinet orwork chamber. The spray of peening particles and metallic powder is thensimply directed at the desired areas of the workpiece. Areas not to becovered can be masked off with various pressure sensitive tapes orrubber or plastic coatings that can be removed easily at a later time.The longer the application time for a given set of conditions thethicker will be the resulting coating. If desired, standard means suchas Almen strips as adopted by the Society of Automotive Engineers may beused for gauging and monitoring the intensity of the peening.Recommended Almen strip arc heights range from 0.002N to 0.012Cdepending on the thicknews and type of material being plated, with thelower values being used for thinner and/or soft substrates and thehigher values for thicker and/or harder substrates. Upon completion ofthe plating operation, the peening particles used may be discarded orreclaimed, as desired. Any unused metallic powder may also be recovered.

In practice, several nozzles could be employed, particularly inautomatic or sequential operations. A part could move automatically intothe spray paths of the several nozzles so prepositioned that all orportions of the part being processed contacts the sprays in the order ofthe desired plating with the nozzles spraying out peening mediaconsisting of small beads and powders so selected to produce a varietyof desired surfaces. The placement of nozzles could be arranged toproduce layering of different plating materials. Additionally, thenozzles could be individiually set to produce different peeningintensities with different peening media. If pre-cleaning is required,the first set of nozzles would spray only the beads, without a powder,prior to any plating being accomplished.

The following examples are included to further describe the invention.

EXAMPLE I In this example the plating process was conducted in a glassbead peening machine comprising an enclosed working cabinet containing ahopper and spray equipment including the nozzle depicted in FIG. 1 ofthe drawing. The nozzle used had an opening diameter of A inch. Analuminum-magnesium alloy plate was placed in the machine 6-8 inches awayfrom the nozzle. In the hopper equal proportions of .0041 to .0021 inchdiameter glass beads and -l00 mesh aluminum powder was mixed and theadmixture spray blasted" under an air pressure of 40-60 psig onto thesurface of the aluminum-magnesium alloy plate. The total blast time forplating, for example, a I X 3 inch aluminummagnesium alloy plate, wasone-half minute. A mechanically worked substrate having a uniformcoating of aluminum of one to two mils thickness thereon was obtained.Photomicrographs of the coated surface cross section at magnificationsof IOOX, and 250X clearly showed the peened nature of the interfaceinterlocking achieved. The resulting aluminum-coated aluminum-magnesiumalloy plate upon testing exhibited increased hardness and compressiveresidual stresses.

EXAMPLE II The procedure of Example I was repeated substituting a steelsubstrate for the aluminum-magnesium alloy. An aluminum-plated steelsubstrate exhibiting similar characteristics was obtained.

EXAMPLE III The procedure of Example I was repeated substituting acopper plate for the aluminum-magnesium alloy plate. An aluminum-coatedcopper plate exhibiting similar characteristics was obtained.

EXAMPLE IV Example I was repeated but with the spray blasting for fiveminutes. A substrate having a substantially thick coating of about fivemils of aluminum, but exhibiting the same desirable characteristics, wasobtained.

EXAMPLE V In this example the same equipment and materials employed inExample I were used except that the nozzle of FIG. 2 was substituted forthe nozzle of FIG. 1 and a separate hopper was provided for the aluminumpowder. The glass beads were first spray blasted" against the steelsubstrate under a pressure of -80 psig in the absence of the aluminumpowder to precondition the substrate surface. After one minute of thisconditioning, the aluminum powder was pressured into the stream of glassbeads at the same rate and the plating phase conducted for a period ofonehalf minute. Results similar to that obtained in Example I wereobserved.

It is claimed:

1. A process for metal plating which comprises spraying a mixture ofmetallic powder and small, solid peening particles at a high velocityagainst a surface, said velocity being sufficient to cause said small,solid peening particles to impact and mechanically bond said metallicpowder onto said surface.

2. The process of claim 1 wherein the small, solid peening particles areselected from the group consisting of glass beads, metal shot, andceramic beads.

3. The process of claim 1 wherein the spraying of the mixture ofmetallic powder and peening particles is effected by air or gaspressure.

4. The process of claim 1 wherein the metallic powder particle size isno larger than one half the peening particle size.

5. The process of claim 1 wherein said metallic powder comprises amixture of dissimilar metallic powders or a mixture of at least onemetallic powder with at least one non-metallic powder.

6. The process of claim 1 wherein the surface plated is selected fromthe group consisting essentially of metal, metal alloy, wood, plasticand ceramic substrates.

7. The process of claim 1, further comprising, prior to spraying saidmixture against said surface, the steps of first preparing said surfaceto be plated by spraying said small, solid peening particles againstsaid surface and then introducing said metallic powder to form saidmixture of solid peening particles and metallic powder.

10. A process for plating which comprises spraying, in the absence ofheat, a mixture including at least one metallic powder and small, solidpeening particles at a high velocity against a surface, said velocitybeing sufficient for said metallic powder to be pounded and bonded tosaid surface by said small, solid peening particles.

2mm?!) 512m? KTATENT WFHIF.

iclas-m Spray Era-casts Using Metallic; Paw'der. ant Peeninq Part PATENTM1 3,154,975 DATED August 28, 1&73

mvH-HEHM Alfred J. Babedkz'i. and Carl L. Baebner it i:: .zrtified fixaierze: appeavs in the r-:9 -idci'- ifiad patent and haf. said LittersPatent are hereby Camus-d shown below:

In the title. "Peen Plating ska-aid refid Me l Pl fiigna-l and sealedthis; 17th day :25 June; 1975.

(SEAL) :tcest:

Attesting, C'fic'rer

2. The prOcess of claim 1 wherein the small, solid peening particles areselected from the group consisting of glass beads, metal shot, andceramic beads.
 3. The process of claim 1 wherein the spraying of themixture of metallic powder and peening particles is effected by air orgas pressure.
 4. The process of claim 1 wherein the metallic powderparticle size is no larger than one half the peening particle size. 5.The process of claim 1 wherein said metallic powder comprises a mixtureof dissimilar metallic powders or a mixture of at least one metallicpowder with at least one non-metallic powder.
 6. The process of claim 1wherein the surface plated is selected from the group consistingessentially of metal, metal alloy, wood, plastic and ceramic substrates.7. The process of claim 1, further comprising, prior to spraying saidmixture against said surface, the steps of first preparing said surfaceto be plated by spraying said small, solid peening particles againstsaid surface and then introducing said metallic powder to form saidmixture of solid peening particles and metallic powder.
 8. The processof claim 7 wherein the surface to be plated is metal and the spraying inthe absence of metallic powder is conducted at an angle to the surfaceand at a peening velocity sufficient to induce compressive stresses intosaid metal substrate.
 9. The process of claim 7 wherein the peeningparticles are selected from glass beads, metal shot and ceramic beads.10. A process for plating which comprises spraying, in the absence ofheat, a mixture including at least one metallic powder and small, solidpeening particles at a high velocity against a surface, said velocitybeing sufficient for said metallic powder to be pounded and bonded tosaid surface by said small, solid peening particles.